Humans are exposed to a large variety of pneumotoxic or carcinogenic chemicals that exert their toxicities after bioactivation of the parent compound by cytochrome P450 enzymes. Lung diseases cause significant morbidity and mortality, and specific P450 enzymes contribute to the etiology of many of these diseases. The selective toxicity to lung tissues is primarily related to the selective expression of P450 genes in bronchiolar or alveolar epithelial cells, without concomitant expression in liver or other tissues. It is also likely that lung-specific expression of certain P450 genetic variants by different individuals leads to differential human susceptibilities to pneumotoxicants, but the molecular mechanisms responsible are not known. The hypothesis of this research is that the selective expression of certain cytochrome P450 genes in human lung epithelial cells is driven by unique, previously uncharacterized transcription factors; these factors act in concert to regulate the expression of the CYP2F1, CYP2S1, CYP3A5, and CYP4B1 genes," and that genetic variability in these genes will contribute to differential susceptibility. The major long-term goal of this research is to precisely determine the factors that regulate the expression of P450 genes in lung cells. This goal will be realized through the following objectives: 1) identify the shared and unique promoter elements of the lung-selective P450 genes and define functional transcriptional control by trans-acting nuclear factors from human lung tissues and cells that bind these core elements; 2) identify and characterize the lung-specific factor (LSF) identified as a CYP2F1 key regulator, along with potential co-regulatory factors and additional related nuclear proteins that form transcriptional complexes with the other lung-selective P450 genes; 3) to demonstrate the functional importance of P450 gene expression in engineered cells through assessment of cellular susceptibility to pneumotoxicants after induction and overexpression of the wild type genes, identified genetic variants, and/or specific trans-acting factors; 4) identify and validate 2F1 and 2S1 genetic variants that may influence intersubject variability to lung toxicities. These studies will provide vital, unique insight concerning the specific mechanisms that control expression of P450 genes in lung cells and will have significant impact on human lung diseases that are caused or exacerbated by toxicant bioactivation by cytochrome P450 enzymes.